Conventional electrochemical sensors generally include an electrochemical element, which has an electrochemical pump cell having a preferably planar, first solid electrolyte body and a first and second preferably porous electrode. These conventional sensors also include an electrochemical sensor cell having a preferably planar, second solid electrolyte body and a third and fourth preferably porous electrode. The sensor has a gas supply opening which includes a gas supply channel which, on the one hand, is connected to a measuring gas chamber, and on the other hand, is connected to a hollow space surrounded by the two solid electrolyte bodies.
A diffusion resistance device, which can contain a porous filling, is arranged in the measuring gas chamber.
The measuring gas arrives in the measuring gas chamber via the gas supply opening and the gas supply channel, the first and the second electrodes of the pump cell acting to regulate the admission of the measuring gas into the gas chamber and thus assure a controlled partial pressure of the gas components to be measured. The electrochemical difference in potential between the electrodes of the second solid electrolyte body arises due to the varying gas partial pressures in the diffusion resistance device and in a reference gas chamber, arranged, for example, in the second solid electrolyte body. The difference in potential can be measured by a voltmeter situated outside the electrochemical element.
The conventional sensors described above, referred to as planar wideband-lambda probes, have been used, for example, in the technology of catalytic exhaust emission control systems for internal combustion engines. A typical design of one such conventional electrochemical sensor is described in German Patent Application No. 38 11 713. The conventional sensors have a disadvantage that they have a so-called lambda=1 ripple, particularly in high operating temperatures. This leads to problems in control processes in which the lambda value represents the control variable. As a result of the ripple of the lambda signal, it is in many cases impossible to make an adjustment for an output quantity value to be sufficiently stable.